Materials

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9 pages, 4263 KiB

Open AccessArticle

Preparation of Ti₃C₂T_x/NiZn Ferrite Hybrids with Improved Electromagnetic Properties

by Xiaobing Zhou, Youbing Li and Qing Huang

Materials 2020, 13(4), 820; https://doi.org/10.3390/ma13040820 - 11 Feb 2020

Cited by 6 | Viewed by 2357

Ti₃C₂T_x/NiZn ferrite composites were synthesized using a co-precipitation hydrothermal method, and further consolidated using electric current field-assisted sintering technology. Nano NiZn ferrites were inserted into the Ti₃C₂T_x interlayers with uniform coverage on [...] Read more.

Ti₃C₂T_x/NiZn ferrite composites were synthesized using a co-precipitation hydrothermal method, and further consolidated using electric current field-assisted sintering technology. Nano NiZn ferrites were inserted into the Ti₃C₂T_x interlayers with uniform coverage on their surfaces. The incorporation of MXenes promoted the sintering kinetics of the NiZn ferrite ceramics. The electrical conductivity increased by six orders of magnitude compared to pure NiZn ferrite ceramics at room temperature. The present work provides a potential way to develop a large family of dense MXenes/ferrite multiphase ceramics. The multiphase ceramics could be potentially used for the on-beam-line higher-order mode load in advanced particle accelerators. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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30 pages, 2136 KiB

Open AccessArticle

Statistical Thermodynamics of Chiral Skyrmions in a Ferromagnetic Material

by Roberto Zivieri

Materials 2019, 12(22), 3702; https://doi.org/10.3390/ma12223702 - 9 Nov 2019

Cited by 9 | Viewed by 2403

Abstract

Solitons are a challenging topic in condensed matter physics and materials science because of the interplay between their topological and physical properties and for the crucial role they play in topological phase transitions. Among them, chiral skyrmions hosted in ferromagnetic systems are axisymmetric [...] Read more.

Solitons are a challenging topic in condensed matter physics and materials science because of the interplay between their topological and physical properties and for the crucial role they play in topological phase transitions. Among them, chiral skyrmions hosted in ferromagnetic systems are axisymmetric solitonic states attracting a lot of attention for their dazzling physical properties and technological applications. In this paper, the equilibrium statistical thermodynamics of chiral magnetic skyrmions developing in a ferromagnetic material having the shape of an ultrathin cylindrical dot is investigated. This is accomplished by determining via analytical calculations for both Néel and Bloch skyrmions: (1) the internal energy of a single chiral skyrmion; (2) the partition function; (3) the free energy; (4) the pressure; and (5) the equation of state of a skyrmion diameters population. To calculate the thermodynamic functions for points (2)–(5), the derivation of the average internal energy and of the configurational entropy is crucial. Numerical calculations of the thermodynamic functions for points (1)–(5) are applied to Néel skyrmions. These results could advance the field of materials science with special regard to low-dimensional magnetic systems. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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9 pages, 2004 KiB

Open AccessArticle

Effect of Defects on Spontaneous Polarization in Pure and Doped LiNbO₃: First-Principles Calculations

by Weiwei Wang, Dahuai Zheng, Mengyuan Hu, Shahzad Saeed, Hongde Liu, Yongfa Kong, Lixin Zhang and Jingjun Xu

Materials 2019, 12(1), 100; https://doi.org/10.3390/ma12010100 - 29 Dec 2018

Cited by 20 | Viewed by 3024

Abstract

Numerous studies have indicated that intrinsic defects in lithium niobate (LN) dominate its physical properties. In an Nb-rich environment, the structure that consists of a niobium anti-site with four lithium vacancies is considered the most stable structure. Based on the density functional theory [...] Read more.

Numerous studies have indicated that intrinsic defects in lithium niobate (LN) dominate its physical properties. In an Nb-rich environment, the structure that consists of a niobium anti-site with four lithium vacancies is considered the most stable structure. Based on the density functional theory (DFT), the specific configuration of the four lithium vacancies of LN were explored. The results indicated the most stable structure consisted of two lithium vacancies as the first neighbors and the other two as the second nearest neighbors of Nb anti-site in pure LN, and a similar stable structure was found in the doped LN. We found that the defects dipole moment has no direct contribution to the crystal polarization. Spontaneous polarization is more likely due to the lattice distortion of the crystal. This was verified in the defects structure of Mg²⁺, Sc³⁺, and Zr⁴⁺ doped LN. The conclusion provides a new understanding about the relationship between defect clusters and crystal polarization. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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14 pages, 6762 KiB

Open AccessArticle

Magneto-Dielectric Behaviour of M-Type Hexaferrite/Polymer Nanocomposites

by Aikaterini Sanida, Sotirios Stavropoulos, Thanassis Speliotis and Georgios C. Psarras

Materials 2018, 11(12), 2551; https://doi.org/10.3390/ma11122551 - 14 Dec 2018

Cited by 26 | Viewed by 3725

Abstract

In the present study two sets of nanocomposites consisting of an epoxy resin and BaFe₁₂O₁₉ or SrFe₁₂O₁₉ nanoparticles were successfully developed and characterized morphologically and structurally via scanning electron microscopy and X-ray diffraction spectra. The dielectric response [...] Read more.

In the present study two sets of nanocomposites consisting of an epoxy resin and BaFe₁₂O₁₉ or SrFe₁₂O₁₉ nanoparticles were successfully developed and characterized morphologically and structurally via scanning electron microscopy and X-ray diffraction spectra. The dielectric response of the nanocomposites was investigated by means of broadband dielectric spectroscopy and their magnetic properties were derived from magnetization tests. Experimental data imply that the incorporation of the ceramic nanoparticles enhances significantly the dielectric properties of the examined systems and their ability to store electrical energy. Dielectric spectra of all systems revealed the presence of three distinct relaxation mechanisms, which are attributed both to the polymer matrix and the nanoinclusions: Interfacial polarization, glass to rubber transition of the polymer matrix and the re-orientation of small polar side groups of the polymer chain. The magnetic measurements confirmed the ferromagnetic nature of the nanocomposites. The induced magnetic properties increase with the inclusion of hexaferrite nanoparticles. The nanocomposites with SrFe₁₂O₁₉ nanoparticles exhibit higher values of coercive field, magnetization, magnetic saturation and remanence magnetization. A magnetic transition was detected in the ZFC/FC curves in the case of the BaFe₁₂O₁₉/epoxy nanocomposites. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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6 pages, 2295 KiB

Open AccessArticle

Magnetic Characterization in the Rayleigh Region of Nanocrystalline Magnetic Cores

by Mikel Osinalde, Pablo Infante, Lurdes Domínguez, Juan Mari Blanco, Alexander Chizhik, Valentina Zhukova, Arcady Zhukov and Julian González

Materials 2018, 11(11), 2278; https://doi.org/10.3390/ma11112278 - 14 Nov 2018

Cited by 4 | Viewed by 2087

Abstract

We report on the structural and magnetic characterization of two nanocrystalline Finemet-type magnetic cores. The nanocrystalline structure developed after annealing the amorphous precursor alloy at 550 °C for 30 and 60 min of annealing time. Structural analysis carried out by means of X-ray [...] Read more.

We report on the structural and magnetic characterization of two nanocrystalline Finemet-type magnetic cores. The nanocrystalline structure developed after annealing the amorphous precursor alloy at 550 °C for 30 and 60 min of annealing time. Structural analysis carried out by means of X-ray diffraction providing useful information on the grain size mean and partial volume of the nanocrystalline phase. The magnetic characterization was focused mainly in the Rayleigh region which, influenced by the intergranular coupling, was found to be more efficient in the sample treated for a longer time with a finer nanocrystalline structure. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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9 pages, 1199 KiB

Open AccessArticle

Single Chiral Skyrmions in Ultrathin Magnetic Films

by Arantxa R. Aranda and Konstantin Y. Guslienko

Materials 2018, 11(11), 2238; https://doi.org/10.3390/ma11112238 - 11 Nov 2018

Cited by 7 | Viewed by 2742

Abstract

The stability and sizes of chiral skyrmions in ultrathin magnetic films are calculated accounting for the isotropic exchange, Dzyaloshinskii–Moriya exchange interaction (DMI), and out-of-plane magnetic anisotropy within micromagnetic approach. Bloch skyrmions in ultrathin magnetic films with B20 cubic crystal structure (MnSi, FeGe) and [...] Read more.

The stability and sizes of chiral skyrmions in ultrathin magnetic films are calculated accounting for the isotropic exchange, Dzyaloshinskii–Moriya exchange interaction (DMI), and out-of-plane magnetic anisotropy within micromagnetic approach. Bloch skyrmions in ultrathin magnetic films with B20 cubic crystal structure (MnSi, FeGe) and Neel skyrmions in ultrathin films and multilayers Co/X (X = Ir, Pd, Pt) are considered. The generalized DeBonte ansatz is used to describe the inhomogeneous skyrmion magnetization. The single skyrmion metastability/instability area, skyrmion radius, and skyrmion width are found analytically as a function of DMI strength

d

. It is shown that the single chiral skyrmions are metastable in infinite magnetic films below a critical value of DMI

d_{c}

, and do not exist at

d > d_{c}

. The calculated skyrmion radius increases as

d

increases and diverges at

d \to d_{c} - 0

, whereas the skyrmion width increases monotonically as

d

increases up to

d_{c}

without any singularities. The calculated skyrmion width is essentially smaller than the one calculated within the generalized domain wall model. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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11 pages, 3627 KiB

Open AccessArticle

Structural and Magnetic Property of Cr³⁺ Substituted Cobalt Ferrite Nanomaterials Prepared by the Sol-Gel Method

by Jinpei Lin, Jiaqi Zhang, Hao Sun, Qing Lin, Zeping Guo, Hu Yang and Yun He

Materials 2018, 11(11), 2095; https://doi.org/10.3390/ma11112095 - 25 Oct 2018

Cited by 21 | Viewed by 2669

Abstract

Cobalt-chromium ferrite, CoCr_xFe_2−xO₄ (x = 0–1.2), has been synthesized by the sol-gel auto-combustion method. X-ray diffraction (XRD) indicates that samples calcined at 800 °C for 3 h were a single-cubic phase. The lattice parameter [...] Read more.

Cobalt-chromium ferrite, CoCr_xFe_2−xO₄ (x = 0–1.2), has been synthesized by the sol-gel auto-combustion method. X-ray diffraction (XRD) indicates that samples calcined at 800 °C for 3 h were a single-cubic phase. The lattice parameter decreased with increasing Cr concentration. Scanning electron microscopy (SEM) confirmed that the sample powders were nanoparticles. It was confirmed from the room temperature Mössbauer spectra that transition from the ferrimagnetic state to the superparamagnetic state occurred with the doping of chromium. Both the saturation magnetization and the coercivity decreased with the chromium doping. With a higher annealing temperature, the saturation magnetization increased and the coercivity increased initially and then decreased for CoCr_0.2Fe_1.8O₄. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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10 pages, 1977 KiB

Open AccessArticle

Modeling the Hysteresis Loop of Ultra-High Permeability Amorphous Alloy for Space Applications

by Michał Nowicki, Roman Szewczyk, Tomasz Charubin, Andriy Marusenkov, Anton Nosenko and Vasyl Kyrylchuk

Materials 2018, 11(11), 2079; https://doi.org/10.3390/ma11112079 - 24 Oct 2018

Cited by 9 | Viewed by 3656

Abstract

This paper presents investigation results regarding the Jiles-Atherton-based hysteresis loop modeling of ultra-high permeability amorphous alloy MELTA^® MM-5Co. The measurement stand is capable of accurately measuring minor and major hysteresis loops for such a material together with exemplary measurement results. The main [...] Read more.

This paper presents investigation results regarding the Jiles-Atherton-based hysteresis loop modeling of ultra-high permeability amorphous alloy MELTA^® MM-5Co. The measurement stand is capable of accurately measuring minor and major hysteresis loops for such a material together with exemplary measurement results. The main source of the measurement error is highlighted, which includes the Earth’s field influence. The results of hysteresis loop modeling with the original Jiles-Atherton model and with two of its modifications are given. In all cases, the parameters of the Jiles-Atherton model were identified in two-step identification on the basis of a differential evolution optimization algorithm. The results indicate that both the original and modified Jiles-Atherton models are suitable for modeling the ultra-soft amorphous alloy. However, the hysteresis model’s parameters vary significantly. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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9 pages, 3461 KiB

Open AccessArticle

First Order Reversal Curve Study of SmFe₂ Melt-Spun Ribbons

by María C. Grijalva-Castillo, Carlos R. Santillán-Rodríguez, Renee J. Sáenz-Hernández, María E. Botello-Zubíate and José A. Matutes-Aquino

Materials 2018, 11(10), 1804; https://doi.org/10.3390/ma11101804 - 22 Sep 2018

Cited by 3 | Viewed by 2957

Abstract

First-order reversal curves (FORC) and the FORC distribution provide a detailed characterization of the relative proportions of reversible and irreversible components of the magnetization of a material, revealing the dominant interactions in the system. Alloys with the nominal composition SmFe₂ were obtained [...] Read more.

First-order reversal curves (FORC) and the FORC distribution provide a detailed characterization of the relative proportions of reversible and irreversible components of the magnetization of a material, revealing the dominant interactions in the system. Alloys with the nominal composition SmFe₂ were obtained by melt-spinning with a cooper wheel velocity of 30 m/s. X-ray powder diffraction analysis showed a greater part consisting of an amorphous phase and a very small amount of SmFe₂ crystalline phase with an average crystallite size of 8 nm. A constant acceleration Mössbauer spectrum, measured at room temperature in transmission mode, was fitted to a continuous distribution of effective fields at the nucleus of the amorphous phase (about 84% of the total area), plus two sextets for the non-equivalent sites of Fe in the SmFe₂ crystalline phase. 91 first-order reversal curves were collected in a Quantum Design PPMS-VSM with reversal fields from –800 mT to +800 mT and using a calibration field of 850 mT. The obtained FORC diagrams showed a combined effect of a local interaction field and a mean interaction field, and showed that the reversible magnetization is a function of both, the applied magnetic field and the irreversible magnetization. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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11 pages, 4430 KiB

Open AccessArticle

Magnetic Properties and Spontaneous Polarization of La-, Mn- and N-Doped Tetragonal BiFeO₃: A First-Principles Study

by Qiuhong Tan, Qianjin Wang and Yingkai Liu

Materials 2018, 11(6), 985; https://doi.org/10.3390/ma11060985 - 11 Jun 2018

Cited by 10 | Viewed by 4032

Abstract

Multiferroic materials have been receiving attention for their potential applications in multifunctional devices. Chemical substitution is an effective method for improving the physical properties of BiFeO₃ (BFO). However, different experimental results have been reported for Lanthanum- (La-) and Manganese (Mn) -doped BFO [...] Read more.

Multiferroic materials have been receiving attention for their potential applications in multifunctional devices. Chemical substitution is an effective method for improving the physical properties of BiFeO₃ (BFO). However, different experimental results have been reported for Lanthanum- (La-) and Manganese (Mn) -doped BFO ceramics. Here, we systematically studied the magnetic properties and spontaneous polarization of La-, Mn-, and Nitrogen (N) -doped tetragonal BiFeO₃ using density functional theory with the generalized gradient approximation and U-value method. The calculated results demonstrated that the systems show ferromagnetism with Mn and N doping, whereas no magnetization was found with La doping in G- and C-type antiferromagnetic orderings. Our research further revealed that the ferromagnetism is attributed to the p-d orbital hybridization. Berry-phase polarization calculations predicted a large polarization of 149.2 µC/cm² along the [001] direction of pure tetragonal BFO. We found that La and N substitution had little influence on the spontaneous polarization, whereas Mn substitution reduced the spontaneous polarization. The reduced energy barrier heights of the doped systems indicate the reduced stability of the off-centering ferroelectricity against the thermal agitation. These findings provide greater understanding for controlling and tuning the multiferroic properties of BFO. Full article

(This article belongs to the Special Issue New Developments in Ferromagnetic Materials)

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